Color processing apparatus and method thereof

ABSTRACT

In order to match the color appearance of the display image on a monitor to that of a print image, the white point of the monitor and that of the viewing light upon viewing the print image are obtained, and a white point upon viewing the display image on the monitor and that upon viewing the print image are calculated using the white point of the monitor, that of the viewing light, and a reference white point. An input color is corrected using the calculated white points. At this time, as the reference white point, a white color which the human visual system perceives as white is used.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a color matching process.

2. Description of the Related Art

In color matching between devices of different types, generally, a colorappearance model such as CIECAM02 which is recommended by the CommissionInternationale de l'Eclairage (CIE) is used. A color appearance modelpredicts color appearances in viewing environments having differentcharacteristics while considering chromatic adaptation.

The human visual system has a function to change its sensitivity so asto adapt to a new environment. For example, when a person moves from aroom illuminated by a fluorescent lamp of a daylight color to a roomilluminated by an incandescent lamp, he or she initially feels theillumination light as yellowish. After a while, however, he or she doesnot feel the yellowishness. This is because the visual sense adapts tothe illumination light, that is, correction action of the visual systemis occurred. This is called chromatic adaptation.

Adaptation of the visual system cannot completely cancel the change ofillumination light. Even when the visual sense chromatically adapts tothe illumination light sufficiently, it does not perceive the color ofthe illumination light as white. This is called incomplete adaptation.

Chromatic adaptation and incomplete adaptation also occur when viewing amonitor. For example, when viewing a monitor whose white point has ahigh color temperature, a person initially feels it as bluish, but lessbluish after a while (chromatic adaptation). However, the bluishnesscannot be completely canceled (incomplete adaptation).

CIECAM02 uses equal energy white (X=Y=Z=100) in a color predictionprocess to perform correction while considering incomplete adaptation.Theoretically, equal energy white is regarded to be perceived as whiteby a human. However, since the color temperature of equal energy whiteis about 5,460K, the human visual system perceives it as a considerablyyellowish color. For this reason, incomplete adaptation cannot beaccurately predicted.

When a display image on a monitor and an output image (printed material)from a printer are placed side by side and viewed, the visual systemtries to adapt to both of the white color of the monitor and that of theviewing light obtained from the ambient light reflected from the printedmaterial. Accordingly, by using an adaptation white point consideringpartial adaptation, the color matching accuracy can be improved.

In Japanese Patent Laid-Open No. 9-093451, a partial adaptation whitecolor for a monitor is obtained from the monitor white color andillumination light white color. On the other hand, as an adaptationwhite color for a printer, a white color without considering partialadaptation is used. That is, the partial adaptation model in JapanesePatent Laid-Open No. 9-093451 considers the influence of theillumination light upon viewing the monitor, but does not consider thatof the monitor upon viewing the printed material. As a result, colormatching with a high accuracy cannot be implemented between a monitorand printer.

SUMMARY OF THE INVENTION

In one aspect, a color processing apparatus for matching a colorappearance of a display image on a monitor to a color appearance of aprint image, comprises: an obtaining section, arranged to obtain a whitepoint of the monitor and a white point of a viewing light upon viewingthe print image; a calculator, arrange to calculate a white point uponviewing the display image on the monitor and a white point upon viewingthe print image using the white point of the monitor, the white point ofthe viewing light, and a reference white point; and a color corrector,arranged to correct an input color using the white points calculated bythe calculator, wherein the reference white point indicates a whitecolor which a human visual system perceives as white.

According to the aspect, upon viewing images in viewing environmentswith different viewing conditions that are placed side-by-side, colormatching with a high accuracy can be performed.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the arrangement of a color processingapparatus of the first embodiment;

FIG. 2 is a flowchart illustrating the image processing in an imageprocessing unit;

FIG. 3 is a view illustrating an example of a user interface forinputting user's instructions;

FIG. 4 is a view schematically showing the relationship among whitepoints in this embodiment;

FIG. 5 is a flowchart for explaining the color processing;

FIG. 6 is a block diagram showing the arrangement of a color processingapparatus of the second embodiment; and

FIG. 7 is a flowchart for explaining the image processing in an imageprocessing unit.

DESCRIPTION OF THE EMBODIMENTS

Color processing of embodiments according to the present invention willbe described in detail hereinafter with reference to the accompanyingdrawings.

First Embodiment

[Arrangement of Apparatus]

FIG. 1 is a block diagram showing the arrangement of a color processingapparatus 101 of the first embodiment.

The color processing apparatus 101 is connected to an image displayapparatus 102 such as a monitor which displays an image and an imageoutput apparatus 104 such as a printer which prints an image.

An image input unit 13 inputs image data of an image displayed on theimage display apparatus 102. An image processing unit 16 performs imageprocessing such as color processing to the image data input by the imageinput unit 13. An image output unit 15 outputs the image data whichunderwent the image processing by the image processing unit 16 to theimage output apparatus 104.

A profile storage unit 21 stores the profiles of the image displayapparatus 102 and image output apparatus 104. A viewing conditionstorage unit 17 stores viewing condition information which indicates theviewing condition of the image display apparatus 102, and viewingcondition information which indicates the viewing condition of a printedmaterial.

A white point obtaining unit 18 obtains white point information whichindicates a white point from the viewing condition information stored inthe viewing condition storage unit 17. A first white point calculationunit 19 calculates a white point for incomplete adaptation correctionfrom the white point information obtained by the white point obtainingunit 18. A second white point calculation unit 20 calculates a whitepoint for partial adaptation correction from the white point forincomplete adaptation correction calculated by the first white pointcalculation unit 19, or the like.

An operation input unit 22 comprises a pointing device such as akeyboard, mouse, touch panel, or the like, and inputs a user'sinstruction to the image processing unit 16.

[Image Processing]

FIG. 2 is a flowchart for explaining the steps of image processingexecuted in the image processing unit 16.

The image processing unit 16 displays a user interface (UI) for settingvarious types of conditions for color matching on a monitor (S200). Themonitor for displaying the UI can be the image display apparatus 102, ormay be separately prepared.

FIG. 3 is a view illustrating an example of the user interface for colormatching setting. A user selects the profile of the image displayapparatus 102 and that of the image output apparatus 104, which aresubject to color matching, from the drop-down menu of a monitor profilesetting section 201 and that of a printer profile setting section 202,respectively. The names or symbols of profiles stored in the profilestorage unit 21 are listed in the drop-down menu.

The user also selects the viewing condition of the image displayapparatus 102 and that of a printed material from the image outputapparatus 104 from the drop-down menu of a monitor viewing conditionsetting section 203 and that of a print viewing condition settingsection 204, respectively. The names or symbols of viewing conditioninformation stored in the viewing condition storage unit 17 are listedin the drop-down menu.

Furthermore, the user operates sliders 205 to 208 to set incompleteadaptation coefficients and partial adaptation coefficients upon viewingthe monitor and the printed material. When color matching setting usingthe UI is complete, the user presses an OK button 209.

When the OK button 209 is pressed, the image processing unit 16 readsthe monitor profile and printer profile set in the monitor profilesetting section 201 and printer profile setting section 202,respectively, from the profile storage unit 21 (S201). In addition, theimage processing unit 16 reads the viewing condition information of themonitor and that of the printed material set in the monitor viewingcondition setting section 203 and print viewing condition settingsection 204, respectively, from the monitor condition storage unit 17(S202).

The white point obtaining unit 18 obtains white point information fromthe viewing condition information read by the image processing unit 16.The first white point calculation unit 19 calculates a white point forincomplete adaptation correction from the white point informationobtained by the white point obtaining unit 18 and the incompleteadaptation coefficients set by the sliders 205 and 207. The white pointcalculation unit 20 calculates a white point for partial adaptationcorrection from the white point for incomplete adaptation correction,the partial adaptation coefficients set by the sliders 206 and 208, andthe like. As the result, the image processing unit 16 obtains the whitepoint for incomplete adaptation correction and that for partialadaptation correction corresponding to the viewing condition of themonitor and that of the printed material, which are designated by theuser (S203).

The image processing unit 16 inputs the image data of an image displayedon the image display apparatus 102 through the image input unit 13(S204). The image processing unit 16 then performs color processing onthe image data using the calorimetric value data of the monitor profile,that of the printer profile, the viewing condition information of themonitor, and that of the printed material, which are designated by theuser, as well as the white points for adaptation correction (S205). Theimage processing unit 16 then outputs the image data, on which the colorprocessing is performed, to the image output apparatus 104 through theimage output unit 15 (S206).

[Calculation of White Point]

FIG. 4 is a view schematically showing the relationship among the whitepoints in this embodiment.

As described above, the human visual system cannot completely correctthe color of a light source upon viewing a monitor, and that of a lightsource upon viewing a printed material as well. Accordingly, it isnecessary to correct incomplete adaptation. In order to accuratelycorrect incomplete adaptation, a white color (indicated by Δ in FIG. 4)which the human visual system senses as whitest should be used as areference white. In the first embodiment, a point on a blackbody locuswith a color temperature of 8,500K is used as the reference white. Thisis based on the result of a test in which a white color is displayed onthe monitor and its color temperature is changed to obtain the whitecolor which a subject feels most preferable. Of course, the referencewhite is not limited to this, and a different white point, e.g., a whitepoint on a daylight locus, which has a color temperature higher thanequal energy white, may be set.

The white point obtaining unit 18 calculates chromaticities u_(Wm) andv_(Wm) of the white point (to be referred to as the monitor white point,hereinafter) of the monitor and chromaticities u_(Wp) and v_(Wp) of thewhite point (to be referred to as the printed material white point) ofthe viewing light obtained from the ambient light reflected by theprinted material, by

u_(Wi)=4·X_(Wi)/(X_(Wi)+15·Y_(Wi)+3·Z_(Wi))

v_(Wi)=6·Y_(Wi)/(X_(Wi)+15·Y_(Wi)+3·Z_(Wi))   (1)

where i=m, p

X_(Wm), Y_(Wm), and Z_(Wm) represent the tristimulus values of themonitor white point, and

X_(Wp), Y_(Wp), and Z_(Wp) represent the tristimulus values of theprinted material white point.

The white point obtaining unit 18 then obtains a color temperatureT_(Wm) of the monitor white point, which corresponds to thechromaticities of the monitor white point, and a color temperatureT_(Wp) of the printed material white point, which corresponds to thechromaticities of the printed material white point, from, e.g., achromaticity-color temperature table stored in the viewing conditionstorage unit 17.

The first white point calculation unit 19 calculates a color temperatureT′_(Wm) of the monitor white point for incomplete adaptation correctionand a color temperature T′_(Wp) of the printed material white point forincomplete adaptation correction by equation (2). Note that a colortemperature T_(Wr) of the reference white point is 8,500K as describedabove.

1/T′_(Wm)={k_(inc) _(—) _(m)·1/T_(Wm)}+{(1−k_(inc) _(—) _(m))·1/T_(Wr})

1/T′_(Wp)={k_(inc) _(—) _(p)·1/T_(Wp)}+{(1−k_(inc) _(—)_(p))·1/T_(Wr})  (2)

where k_(inc) _(—) _(i) is an incomplete adaptation coefficient, and

0≦k_(inc) _(—) _(i) ≦1

Note that the value set by the user in the color matching setting UIdescribed above is utilized as the incomplete adaptation coefficient,but it can be automatically delivered using a function or the like. Thereciprocal of the color temperature is used for the calculationdescribed above for the following reason. That is, the difference incolor temperature does not correspond to the color difference perceivedby humans, but the reciprocal of the color temperature substantiallycorresponds to the human perception.

By using the white points of the color temperatures obtained by equation(2), it is possible to accurately correct incomplete adaptation andaccurately predict color appearances upon separately viewing the monitorand printed material. Note that, when viewing the monitor and printedmaterial at the same time, the adaptation state is different from thatwhen viewing them separately. In this case, it is considered that theprinted material white point affects color appearance when viewing themonitor, and the monitor white point affects color appearance whenviewing the printed material.

To solve this problem, the second white point calculation unit 20calculates a color temperature T″_(Wm) of the monitor white point forpartial adaptation correction and a color temperature T″_(Wp) of theprinted material white point for partial adaptation correction whileconsidering partial adaptation, by:

1/T″_(Wm)=(Km·L*_(m)·1/T′_(Wm)−Km′·L*_(p)·1/T′_(Wp))/(Km·L*_(m)+Km′·L*p)

1/T″_(Wp)=(Kp·L*_(p)·1/T′_(Wp)−Kp′·L*m·1/T′_(Wm))/(Kp·L*_(p)+Kp′·L*_(m))  (3)

where Ki=k<sub>mix_i</sub> is a partial adaptation coefficient,

Ki==1−Ki

0≦Ki≦1

L*_(i) is a weighting coefficient based on the luminance of the whitepoint.

Note that the value set by the user in the color matching setting UIdescribed above is utilized as the partial adaptation coefficient, butit can be automatically delivered using a function or the like. Based onthe idea that the human visual system adapts to the white point with ahigher luminance, the weighting coefficient L*_(i) is delivered by:

if Y_(Wm)≦Y_(Wp), then L*_(m)=116.0×(Y_(Wm)/Y_(Wp))^(1/3)−16.0 elseL*_(m)=100

if Y_(Wp)≦Y_(Wm), then L*_(m)=116.0×(Y_(Wp)/Y_(Wm))^(1/3)−16.0 elseL*_(m)=100   (4)

The second white point calculation unit 20 calculates chromaticitiesu″_(Wm) and v″_(Wm) corresponding to the color temperature of themonitor white point for partial adaptation correction and chromaticitiesu″_(Wp) and v″_(Wp) corresponding to the color temperature of theprinted material white point for partial adaptation correction, by usingthe chromaticity-color temperature table described above. The secondwhite point calculation unit 20 then calculates tristimulus valuesX″_(Wm)Y″_(Wm)Z″_(Wm) of the monitor white point for partial adaptationcorrection by:

if Y_(Wm)≦Y_(Wp), then Y″_(Wm)={(L*″_(Wm)+16.0)/116.0}³·Y_(Wp)

else Y″_(Wm)=Y_(Wm)

X″_(Wm)=(3.0/2.0)·(u″_(Wm)/v″_(Wm))·Y″_(Wm)

Z″_(Wm)=(4.0·X″_(Wm)/u″_(Wm)−X″_(Wm)−15.0·Y″_(Wm))/3.0   (5)

where L*″_(Wm)=L*_(m)·k_(m)+100.0(1−k_(m))

The second white point calculation unit 20 also calculates a tristimulusvalue X″_(Wp)Y″_(Wp)Z″_(Wp) of the printed material white point forpartial adaptation correction by:

if Y_(Wp)≦Y_(Wm), then Y″_(Wp)={(L*″_(Wp)+16.0)/116.0}³·Y_(Wm)

else Y″_(Wp)=Y_(Wp)

X″_(Wp)=(3.0/2.0)·(u″_(Wp)/v_(Wp))·Y″_(Wp)

Z″_(Wp)=(4.0·X″_(Wp)/u″_(Wp)−X″_(Wp)−15.0·Y″_(Wp))/3.0   (6)

where L*″_(Wp)=L*_(p)·k_(p)+100.0(1−k_(p))

[Color Processing]

FIG. 5 is a flowchart for explaining the color processing (S205).

The image processing unit 16 obtains the data described in the monitorprofile, which indicates the relationship between the device RGB valuesand XYZ values of a grid point (S501). The image processing unit 16 thenconverts the XYZ values of each grid point into JCh values by usingCIECAM02 forward conversion based on the monitor white point for partialadaptation correction (S502). Note that CIECAM02 is used for chromaticadaptation conversion, but the chromatic adaptation conversion is notlimited to this. Another conversion formula such as the Von Krieschromatic adaptation formula or the like may be used.

The color processing unit 16 performs calorimetric gamut mapping of theJCh values of each grid point (S503). Since the shape of a monitor gamutis different from that of a printer gamut, the gamut mapping maps acolor outside the printer gamut onto the printer gamut. Generally, whenit is desired to maintain the color appearance as much as possible, suchas in color matching between the monitor and printer, colorimetric gamutmapping is desirable. Colorimetric gamut mapping is a technique inwhich, for example, a color within the printer gamut is not mapped, buta color outside the printer gamut is mapped to the point closest to theboundary of the printer gamut. Gamut mapping is not limited tocolorimetric one, and another method may be used.

The color processing unit 16 converts the mapped JCh values into XYZvalues by using CIECAM02 inverse conversion based on the printedmaterial white point for partial adaptation correction (S504). The colorprocessing unit 16 then converts the XYZ values into the device RGBvalues of the image output apparatus 104 by using the printer profile(S505).

The color processing unit 16 generates a lookup table (LUT) as colorprocessing data for associating the monitor device RGB values of eachgrid point with the corresponding device RGB values of the image outputapparatus 104 (S506). The color processing unit 16 converts the RGBvalues of the image data input in step S204 into the device RGB value ofthe image output apparatus 104 by using the generated LUT and aninterpolation operation such as tetrahedron interpolation, therebygenerating the image data to be supplied to the image output apparatus104 (S507).

In this manner, incomplete adaptation is accurately corrected, and ahuman-adaptable white point is also accurately obtained whileconsidering the mutual influence of the monitor and viewing light uponviewing both the display image on the monitor and the printed material.Therefore, it is possible to color-match the color appearance of thedisplay image on the monitor to that of the printed material with a highaccuracy.

Second Embodiment

Color Processing of the Second Embodiment according to the presentinvention will be described below. Note that the same components as inthe first embodiment will be designated by the same reference numeralsin the second embodiment, and a detailed description will not berepeated.

FIG. 6 is a block diagram showing the arrangement of a color processingapparatus 101 of the second embodiment.

The color processing apparatus 101 of the second embodiment comprisessensors 27 and 28 and a viewing condition obtaining unit 29, in place ofthe viewing condition storage unit 17 of the first embodiment shown inFIG. 1.

The sensor 27 measures the monitor light of an image display apparatus102. The sensor 28 measures the light of the environment in which aprinted material from an image output apparatus 104 is viewed. Thesensors 27 and 28 measure the tristimulus values of the white point ofthe monitor light and those of the white point of the ambient light,respectively, by using, e.g., a spectral radiancementer. Note that it isalso possible to provide one sensor and moves it depending on the lightto be measured. The viewing condition obtaining unit 29 obtains theinformation of ambient light measured by the sensors 27 and 28, undercontrol of an image processing unit 16.

FIG. 7 is a flowchart illustrating the image processing in the imageprocessing unit 16.

The image processing unit 16 displays a UI (S200), obtains profiles(S201), and then controls the viewing condition obtaining unit 29 toobtain the tristimulus values of the monitor light and ambient light(S702). The image processing unit 16 updates the profiles by theobtained tristimulus values of the monitor light and ambient light(S703).

After that, as in the first embodiment, the image processing unit 16obtains white points for incomplete adaptation correction and those forpartial adaptation correction (S203), inputs image data (S204), performscolor processing (S205), and outputs the image data which underwent thecolor processing (S206).

According to this arrangement, the same effect as in the firstembodiment can be obtained. In addition, it is possible to accuratelyfind the white point of the monitor light and that of the ambient light,thereby performing color matching with a higher accuracy.

Modification of Embodiments

A case in which a display image on a monitor and an output image(printed material) from a printer are placed side by side and viewed hasbeen described above. However, with reference to the above description,those skilled in the art can readily apply the above-describedembodiments to another viewing situation.

An example of another viewing situation is a case in which monitors withdifferent characteristics are placed side by side and the display imageson the respective monitors are viewed. In this case, differences indisplay characteristics of the monitors, ambient light, viewing positionof the observer, and the like serve as the different viewing conditions.

Document sheets or printed materials may be placed side by side in thedifferent viewing environments, and a document sheet and printedmaterial or two printed materials may be viewed. When viewing the twoprinted materials, an identical printer or printers of different typescan be used. When the types of printers are different, the deviceprofiles of the respective printers are used to perform color matching,as in proofing.

In addition, a document image may be photographed by a digital camera orread by a scanner, and the document image (display image) displayed on amonitor and the document sheet may be placed side by side and viewed. Inthis case, the device profile of the scanner and that of the monitor areused to perform color matching.

Exemplary Embodiments

The present invention can be applied to a system constituted by aplurality of devices (e.g., host computer, interface, reader, printer)or to an apparatus comprising a single device (e.g., copying machine,facsimile machine).

Further, the present invention can provide a storage medium storingprogram code for performing the above-described processes to a computersystem or apparatus (e.g., a personal computer), reading the programcode, by a CPU or MPU of the computer system or apparatus, from thestorage medium, then executing the program.

In this case, the program code read from the storage medium realizes thefunctions according to the embodiments.

Further, the storage medium, such as a floppy disk, a hard disk, anoptical disk, a magneto-optical disk, CD-ROM, CD-R, a magnetic tape, anon-volatile type memory card, and ROM can be used for providing theprogram code.

Furthermore, besides above-described functions according to the aboveembodiments can be realized by executing the program code that is readby a computer, the present invention includes a case where an OS(operating system) or the like working on the computer performs a partor entire processes in accordance with designations of the program codeand realizes functions according to the above embodiments.

Furthermore, the present invention also includes a case where, after theprogram code read from the storage medium is written in a functionexpansion card which is inserted into the computer or in a memoryprovided in a function expansion unit which is connected to thecomputer, CPU or the like contained in the function expansion card orunit performs a part or entire process in accordance with designationsof the program code and realizes functions of the above embodiments.

In a case where the present invention is applied to the aforesaidstorage medium, the storage medium stores program code corresponding tothe flowcharts described in the embodiments.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2007-117624, filed Apr. 26, 2007, which is hereby incorporated byreference herein in its entirety.

1. A color processing apparatus for matching a color appearance of a display image on a monitor to a color appearance of a print image, comprising: an obtaining section, arranged to obtain a white point of the monitor and a white point of a viewing light upon viewing the print image; a calculator, arrange to calculate a white point upon viewing the display image on the monitor and a white point upon viewing the print image using the white point of the monitor, the white point of the viewing light, and a reference white point; and a color corrector, arranged to correct an input color using the white points calculated by said calculator, wherein the reference white point indicates a white color which a human visual system perceives as white.
 2. The apparatus according to claim 1, wherein the reference white point is a point on a blackbody locus.
 3. The apparatus according to claim 1, wherein said calculator uses for the calculation a weight corresponding to a lightness of the white point of the monitor and a lightness of the white point of the viewing light.
 4. The apparatus according to claim 1, wherein said obtaining section further obtains a monitor incomplete adaptation coefficient, a monitor partial adaptation coefficient, a print incomplete adaptation coefficient, and a print partial adaptation coefficient, and said calculator calculates the white point upon viewing the display image on the monitor by using the white point of the monitor, the white point of the viewing light, the reference white point, the monitor incomplete adaptation coefficient, and the monitor partial adaptation coefficient, and calculates the white point upon viewing the print image by using the white point of the monitor, the white point of the viewing light, the reference white point, the print incomplete adaptation coefficient, and the print partial adaptation coefficient.
 5. A color processing method of matching a color appearance of a display image on a monitor to a color appearance of a print image, comprising the steps of: obtaining a white point of the monitor and a white point of a viewing light upon viewing the print image; calculating a white point upon viewing the display image on the monitor and a white point upon viewing the print image using the white point of the monitor, the white point of the viewing light, and a reference white point; and correcting an input color using the white points calculated by said calculator, wherein the reference white point indicates a white color which a human visual system perceives as white.
 6. The method according to claim 5, wherein the reference white point is a point on a blackbody locus.
 7. The method according to claim 5, wherein the calculating step uses for the calculation a weight corresponding to a lightness of the white point of the monitor and a lightness of the white point of the viewing light.
 8. The method according to claim 5, wherein the obtaining step further obtains a monitor incomplete adaptation coefficient, a monitor partial adaptation coefficient, a print incomplete adaptation coefficient, and a print partial adaptation coefficient, and the calculating step calculates the white point upon viewing the display image on the monitor by using the white point of the monitor, the white point of the viewing light, the reference white point, the monitor incomplete adaptation coefficient, and the monitor partial adaptation coefficient, and calculates the white point upon viewing the print image by using the white point of the monitor, the white point of the viewing light, the reference white point, the print incomplete adaptation coefficient, and the print partial adaptation coefficient.
 9. A computer-readable storage medium storing a computer-executable program causing a computer to perform a color processing method, the method comprising the step of: obtaining a white point of the monitor and a white point of a viewing light upon viewing the print image; calculating a white point upon viewing the display image on the monitor and a white point upon viewing the print image using the white point of the monitor, the white point of the viewing light, and a reference white point; and correcting an input color using the white points calculated by said calculator, wherein the reference white point indicates a white color which a human visual system perceives as white.
 10. The medium according to claim 9, wherein the reference white point is a point on a blackbody locus.
 11. The medium according to claim 9, wherein the calculating step uses for the calculation a weight corresponding to a lightness of the white point of the monitor and a lightness of the white point of the viewing light.
 12. The medium according to claim 9, wherein the obtaining step further obtains a monitor incomplete adaptation coefficient, a monitor partial adaptation coefficient, a print incomplete adaptation coefficient, and a print partial adaptation coefficient, and the calculating step calculates the white point upon viewing the display image on the monitor by using the white point of the monitor, the white point of the viewing light, the reference white point, the monitor incomplete adaptation coefficient, and the monitor partial adaptation coefficient, and calculates the white point upon viewing the print image by using the white point of the monitor, the white point of the viewing light, the reference white point, the print incomplete adaptation coefficient, and the print partial adaptation coefficient. 